In China, the tree of heaven has a long and rich history. It was mentioned in the oldest extant Chinese dictionary and listed in countless Chinese medical texts for its purported ability to cure ailments ranging from mental illness to balding. The roots, leaves and bark are still used today in traditional Chinese medicine, primarily as an astringent. The tree has been grown extensively both in China and abroad as a host plant for the ailanthus silkmoth, a moth involved in silk production. Ailanthus has become a part of western culture as well, with the tree serving as the central metaphor and subject matter of the best-selling American novel '''' by Betty Smith.
The tree was first brought from China to Europe in the 1740s and to the United States in 1784. It was one of the first trees brought west during a time when ''chinoiserie'' was dominating European arts, and was initially hailed as a beautiful garden specimen. However, enthusiasm soon waned after gardeners became familiar with its habits and its foul smelling odour. Despite this, it was used extensively as a street tree during much of the 19th century. Outside of Europe and the United States, the plant has been spread to many other areas beyond its native range. In a number of these, it has become an invasive species due to its ability to quickly colonise disturbed areas and suppress competition with chemicals. It is considered a noxious weed in Australia, the United States, New Zealand and several countries in and eastern Europe. The tree also vigorously when cut, making its eradication difficult and time consuming.
Description
''A. altissima'' is a medium-sized tree that reaches heights between 17 and 27 metres with a diameter at breast height of about 1 metre . The bark is smooth and light grey, often becoming somewhat rougher with light tan fissures as the tree ages. The twigs are stout, smooth to lightly pubescent, and reddish or chestnut in colour. They have lenticels as well as heart-shaped leaf scars with many bundle scars around the edges. The buds are finely pubescent, dome shaped, and partially hidden behind the , though they are completely visible in the dormant season at the sinuses of the leaf scars.
The are large, odd- or even-pinnately compound, and arranged alternately on the stem. They range in size from 30 to 90 cm in length and contain 10-41 leaflets organised in pairs, with the largest leaves found on vigorous young sprouts. The rachis is light to reddish-green with a swollen base. The leaflets are with entire margins, somewhat asymmetric and occasionally not directly opposite to each others. Each leaflet is 5 to 18 cm long and 2.5 to 5 cm wide. They have a long tapering end while the bases have two to four teeth, each containing one or more glands at the tip. The leaflets' upper sides are dark green in colour with light green veins, while the undersides are a more whitish green. The petioles are 5 to 12 mm long. They appear from mid-April in the south of its range to July in the north. ''A. altissima'' is , with male and female flowers being borne on different individuals. Male trees produce three to four times as many flowers as the females, making the male flowers more conspicuous. Furthermore, the male plants emit a foul-smelling odour while flowering to attract pollinating insects. Female flowers contain ten sterile stamens with heart-shaped anthers. The pistil is made up of five free carpels , each containing a single ovule. Their are united and slender with star-shaped s. ''Altissima'' is for "tallest", and refers to the sizes the tree can reach. The plant is sometimes incorrectly cited with the specific epithet in the masculine , which is incorrect since botanical, like Classical Latin, treats most tree names as feminine.
There are three of ''A. altissima'':
*''A. altissima'' var. ''altissima'', which is the type variety and is native to mainland China.
*''A. altissima'' var. ''tanakai'', which is endemic to northern Taiwan highlands. It differs from the type in having yellowish bark, odd-pinnate leaves that are also shorter on average at 45 to 60 cm long with only 13-25 scythe-like leaflets. It is listed as endangered in the IUCN Red List of threatened species due to loss of habitat for building and industrial plantations.
*''A. altissima'' var. ''sutchuenensis'', which differs in having red branchlets. and northern Korea. Within China itself it has also been naturalised beyond its native range in areas such as Qinghai, Ningxia and Xinjiang. The tree was separately brought to California in the 1890s by Chinese immigrants who came during the California Gold Rush. It has escaped cultivation in all areas where it was introduced, but most extensively in the United States. Ailanthus has also been introduced to Argentina, New Zealand, the Middle East and in some countries in South Asia such as Pakistan.
In North America, ''A. altissima'' is present from Massachusetts in the east, west to southern Ontario, southwest to Iowa, south to Texas, and east to the north of Florida. On the west coast it is found from New Mexico west to California and north to Washington. Similarly, another study conducted in southwestern Virginia determined that the tree of heaven is thriving along approximately 30% of the state's interstate highway system length or mileage. It sometimes enters undisturbed areas as well and competes with native plants.
Ecology
Ailanthus is an opportunistic plant that thrives in full sun and disturbed areas. It spreads aggressively both by seeds and vegetatively by root sprouts. It can re-sprout rapidly after being cut. though it is sometimes found competing with hardwoods, but such competition rather indicates it was present at the time the stand was established. It is a short lived tree in any location and rarely lives more than 50 years. The inhibitors are strongest in the bark and roots, but are also present in the leaves, wood and seeds of the plant. One study showed that a crude extract of the root bark inhibited 50% of a sample of garden cress seeds from germinating. The same study tested the extract as an herbicide on garden cress, redroot pigweed , velvetleaf , yellow bristlegrass , barnyard grass , pea and maize . It proved able to kill nearly 100% of seedlings with the exception of velvetleaf, which showed some resistance. Another experiment showed a water extract of the chemical was either lethal or highly damaging to 11 North American hardwoods and 34 conifers, with the white ash being the only plant not adversely affected. The chemical does not, however, affect the tree of heaven's own seedlings, indicating that ''A. altissima'' has a defence mechanism to prevent autotoxicity.
The tree of heaven is a very rapidly growing tree, possibly the fastest growing tree in North America. Growth of one to two metres per year for the first four years is considered normal. Shade considerably hampers growth rates. Older trees, while growing much slower, still do so faster than other trees. Studies found that Californian trees grew faster than their counterparts, and American trees in general grew faster than Chinese ones. In its native range ''A. altissima'' is associated with at least 32 species of arthropods and 13 species of fungi.
Uses
In addition to its use as an ornamental plant, the tree of heaven is also used for its wood, medicinal properties, and as a host plant to feed silkworms of the moth ''Samia cynthia'', which produces silk that is stronger and cheaper than mulberry silk, although with inferior gloss and texture. It is also unable to take dye. This type of silk is known as "pongee" or "Shantung silk", the second name being derived from Shandong Province in China where this silk is often produced. Its production is particularly well known in the Yantai region of that province. The moth has also been introduced in the United States. There are problems with using the wood as lumber, however. Because the trees exhibit rapid growth for the first few years, the trunk has uneven texture between the inner and outer wood, which can cause the wood to twist or crack during drying. Techniques have been developed for drying the wood so as to prevent this cracking, allowing it to be commercially harvested. Although the live tree tends to have very flexible wood, the wood is quite hard once properly dried.
Cultivation
Tree of heaven is a popular ornamental tree in China and valued for its tolerance of difficult growing conditions.In Europe, however, the tree is still used in the garden to some degree as its habit is generally not as invasive as it is in America. In the United Kingdom it is especially common in London squares, streets, and parks, though it is also frequently found in gardens of southern England and East Anglia. It becomes rare in the north, occurring only infrequently in southern Scotland. It is also rare in Ireland. In Germany the tree is commonly planted in gardens. The tree has furthermore become unpopular in cultivation in the west due to the fact that it is short-lived and that the trunk soon becomes hollow, making trees more than two feet in diameter unstable in high winds.
A few cultivars exist, but they are not often sold outside of China and probably not at all in North America:
*‘Hongye’ - The name is Chinese and means "red leaves". As the name implies it has attractive vivid red foliage
*‘Metro’ - A male cultivar with a tighter crown than usual and a less weedy habit
Medicinal
Nearly every part of ''A. altissima'' has some application in Chinese traditional medicine. One of the oldest recipes, recorded in a work from 732 AD, is used for treating mental illness. It involved chopped root material, young boys' urine and douchi. After sitting for a day the liquid was strained out and given to the patient over the course of several days.
The s are also used in modern Chinese medicine under the name ''feng yan cao'' , meaning "herbal phoenix eye". They are used as a hemostatic agent, spermatorrhea and for treating patients with blood in their feces or urine. It was clinically shown to be able to treat trichomoniasis, a vaginal infection caused by the protozoan ''Trichomonas vaginalis''.
Anecdotal evidence suggests that the plant may be mildly toxic. The noxious odours have been associated with nausea and headaches, as well as with contact dermatitis reported in both humans and sheep, who also developed weakness and paralysis. It contains a quinone irritant, 2,6-dimethoxybenzoquinone, as well as active quassinoids which may account for these effects, but they have, however, proved difficult or impossible to reproduce in humans and goats. In one trial a tincture from the blossom and foliage caused nausea, vomiting and muscular relaxation.
Culture
China
In addition to the tree of heaven's various uses, it has also been a part of Chinese culture for many centuries and has more recently attained a similar status in the west. Within the oldest extant Chinese dictionary, the Erya, written in the 3rd century BC, the tree of heaven is mentioned second among a list of trees. It was mentioned again in a materia medica compiled during the Tang dynasty in 656 AD. Each work favoured a different character, however, and there is still some debate in the Chinese botanical community as to which character should be used. The current name, ''chouchun'' , means "stinking spring", and is a relatively new appellation. People living near the lower Yellow River know it by the name ''chunshu'' , meaning "spring tree". The name stems from the fact that ''A. altissima'' is one of the last trees to come out of dormancy, and as such its leaves coming out would indicate that winter was truly over. In certain parts of the United States, the species is called ghetto palm because of its propensity for growing in the inhospitable conditions of urban areas, or on abandoned and poorly maintained properties.
Until March 26, 2008, a -tall member of the species was a prominent "centerpiece" of the sculpture garden at the Noguchi Museum in the borough of Queens in New York City. The tree had been spared by the sculptor Isamu Noguchi when in 1975 he bought the building which would become the museum and cleaned up its back lot. The tree was the only one he left in the yard, and the staff would eat lunch with Noguchi under it. "n a sense, the sculpture garden was designed around the tree", said a former aide to Noguchi, Bonnie Rychlak, who later became the museum curator. By 2008, the old tree was found to be dying and in danger of crashing into the building, which was about to undergo a major renovation. The museum hired the Detroit Tree of Heaven Woodshop, an artists' collective, to use the wood to create benches, sculptures and other amenities in and around the building. The tree's rings were counted, revealing its age to be 75, and museum officials hoped it would regenerate from a stump, as these trees often do.
Europe
Ingo Vetter, a German artist and professor of fine arts at Umea University in Sweden, was influenced by the idea of the "ghetto palm" and installed a living ailanthus tree taken from Detroit for an international art show called ''Shrinking Cities'' at the KW Institute of Contemporary Art in Berlin in 2004.
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